1. Field of the Invention
The present invention relates to a method of welding wound cores of substantially amorphous ribbons and a wound core made thereby.
2. Description of the Prior Art
Wound cores of amorphous alloy ribbons made by rapid quenching have increasingly been used for varieties of applications, among other things, choke coils, filters, saturable reactors, etc.
Amorphous wound cores are in general heat-treated and encased in nonmagnetic cases usually made of plastics. Alternatively, they may be impregrated with resins. Since they are constituted by ribbons, however, they tend to loosen and the ribbon ends are likely to be separated from the wound core bodies, unless the ribbon ends are fastened to the core bodies. Accordingly, some measures should be taken to prevent the above problems from occurring until the wound cores are contained in cases or impregnated with resins.
Japanese Patent Laid-Open No. 53-65238 discloses a process for welding at least two glassy metal bodies by clamping overlapped portions of the bodies between electrodes and applying a clamping force to the overlapped portions, supplying an electrical current having a rapid decay to the electrodes to melt metal body portions through which the current passes, and extracting heat from the bodies through the electrodes to cool the bodies at a rate of at least 10.sup.5 .degree. C./sec by employing high conductivity electrodes. Thanks to quick removal of heat generated by welding, welds are kept substantially glassy. In this process, however, a clamping force is applied to the wound ribbons so that internal stress remains in the welds. This deteriorates magnetic properties of the wound cores. In particular, the coercivity of the wound cores increases due to the internal stress remaining therein. The larger the coercivity of wound cores, the more the loss thereof when used. Furthermore, when three or more ribbon layers are to be welded, this method does not work well due to large contact resistance between the ribbons clamped between the two electrodes. Accordingly, this process is not considered effective for welding wound cores of many turns.
The use of laser ray has been proposed to weld laminated amorphous alloy sheets constituting magnetic head core chips. Welding is performed on the periphery of the laminated sheets. This may be suitable for welding the sheets laminated into integral bodies like magnetic core chips. It is, however, not necessarily suitable for welding amorphous wound cores which should have as small welded areas as possible. Further, wound cores need not be welded from the outermost ribbons to the innermost ribbons. Accordingly, it may be said that the laser welding method unnecessarily causes too much deterioration of magnetic characteristics. In addition, the laser welding method is generally expensive and should be performed carefully so as to avoid dangerous accidents.
An object of the present invention is, therefore, to provide a method for welding amorphous wound cores economically without deteriorating the magnetic characteristics thereof.